Unraveling the Complex Delithiation Mechanisms of Olivine-Type Cathode Materials, LiFe x Co 1– x PO 4
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, U.K.
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, U.K., Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, United States
The delithiation mechanisms occurring within the olivine-type class of cathode materials for Li-ion batteries have received considerable attention because of the good capacity retention at high rates for LiFePO4. A comprehensive mechanistic study of the (de)lithiation reactions that occur when the substituted olivine-type cathode materials LiFe$$_x$$Co1–$$_x$$PO4 ($$x$$ = 0, 0.05, 0.125, 0.25, 0.5, 0.75, 0.875, 0.95, 1) are electrochemically cycled is reported here using in situ X-ray diffraction (XRD) data and supporting ex situ 31P NMR spectra. On the first charge, two intermediate phases are observed and identified: Li1–$$_x$$(Fe3+)$$_x$$(Co2+)1–$$_x$$PO4 for $0 < x < 1$ (i.e., after oxidation of Fe2+ to Fe3+) and Li2/3Fe$$_x$$Co1–$$_x$$PO4 for $0 ≤ x ≤ 0.5$ ($i.e.$, the Co-majority materials). For the Fe-rich materials, we study how nonequilibrium, single-phase mechanisms that occur discretely in single particles, as observed for LiFePO4 at high rates, are affected by Co substitution. In the Co-majority materials, a two-phase mechanism with a coherent interface is observed, as was seen in LiCoPO4, and we discuss how it is manifested in the XRD patterns. We then compare the nonequilibrium, single-phase mechanism with the bulk single-phase and coherent interface two-phase mechanisms. Despite the apparent differences between these mechanisms, we discuss how they are related and interconverted as a function of Fe/Co substitution and the potential implications for the electrochemistry of this system.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Northeastern Center for Chemical Energy Storage (NECCES)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- SC0001294
- OSTI ID:
- 1257503
- Alternate ID(s):
- OSTI ID: 1371400
- Journal Information:
- Chemistry of Materials, Journal Name: Chemistry of Materials Vol. 28 Journal Issue: 11; ISSN 0897-4756
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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